(1) Field of the Invention
The present invention relates generally to plug pulling machines, and in particular, to machines for pulling plugs from Integrated Chip (IC) tubes in semiconductor manufacturing lines.
(2) Description of the Related Art
Machines for pulling plugs from conduits of different types and shapes, and used in many different applications are well known in their specific areas of interest. Plugs in most cases are completely disposed in a tube. Cork plugs in wine bottles are well known in this respect. And so are cork plugs for champagne bottles, but which, unlike with wine corks, generally protrude from the mouth of the champagne bottle with a bulbous portion. Heat exchanger tubes in general, and those in nuclear powered steam generators in particular are also equipped with plugs that are completely disposed in the tubes. These plugs have an explosive device such that when the heat-exchanger malfunctions, the explosive in the plug is activated and the plug is forced into close contact with the inside of the tube, thus blocking flow of the heat-exchanging fluid in the affected tube. As is known in the art, the fluid flowing inside the tube exchanges heat with the fluid flowing outside the tube. Occasionally a tube can become defective and leak, resulting in commingling of the two fluids. This is not desirable especially when radioactive materials leak from the heat exchanger of nuclear steam generators. And hence, when a leak occurs, the heat exchanger tube is plugged so that the fluid is not permitted to flow through the tube.
Plugs so disposed in tubes must be removed for recycling of the tubes. In the case with wine bottles, the cork plug is removed by piercing it with a cork-screw, screwing into the cork and then pulling the cork-screw out, and hence the cork with it, by any number of well-known techniques such as leveraging a sleeve of the cork-screw device against the mouth of the bottle. Plugs from heat exchanger tubes are actually drilled out as described in U.S. Pat. No. 4,734,972. More specifically, the tube plug removal machine of this Patent removes any type of tube plug by drilling into a plug portion with a threaded section of the tap drill bit after the drilled hole has been threaded by a tapping section thereof, and removing a portion of the tube holding the plug in the tube with a counterbore drill bit mounted concentrically about the tap drill bit. After a portion of the plug has been removed by the counterbore drill bit, pulling on the tap drill bit removes the remaining plug portion from the tube.
In other methods of prior art for easier removal of plugs from conduits employ not only static pulling on the plug, but also repetitive impulsive forces as well. Such a method disclosed is in U.S. Pat. No. 5,465,483. The method as described in this Patent is particularly suited to removing a plug from a heat-exchanger tube in a nuclear powered steam generator. For this purpose, two hydraulic actuators are used: one for moving an expansion member out of engagement with an interior plug wall, a second capable of attachment to the plug for applying a static pull force to the plug, and an arrangement connecting an air impact tool to the second hydraulic actuator for applying, simultaneously with the static force, high-frequency impulses to the plug.
A still another approach is adopted in some prior art methods for removing plugs from conduits. The plug itself is modified. Thus in U.S. Pat. No. 5,255,717, Nelson, et al. disclose an improved plug comprising a cylindrical shell having tapered sidewalls, a closed end, and open end, a cork-shaped expander element disposed within the shell that radially expands the tapered sidewalls of the shell into sealing engagement with the inner walls of a tube when axially drawn from the closed to the open end of the shell. The plug removal is accomplished by an expander remover that axially pushes the expander element backward against the closed end of the shell.
It will be appreciated by those skilled in the art of handling tubes containing integrated circuit, or IC, packages that the methods described above cannot be used to advantage on a semiconductor manufacturing line. Firstly, IC tubes are generally comprised of cylindrical or prismatic conduits of relatively thin plastic material. The tubes are used to transport fragile IC packages including dual-in-line packages (DIP), leadless-chip-carriers (LLCC), small-outline packages (SOP) and small-outline-j-lead packages (SOJ). Secondly, the plugs used are also of plastic material. The methods of prior art for pulling plugs out of IC tubes would damage the contents irreparably. Therefore, what is needed is a simple machine for pulling plugs out of IC tubes automatically.